Hi! Brian from Warmoth here.
We did an all-ebony 5-string bass a while back (the customer sent us wood for the body) - I believe the body alone was around 15lbs. The customer said he loves it, though, and we never heard any complaints. Though of course I have a theory that he's now too hunched over to pick up the phone and call us.
I think I remember Harry Fleishman saying he had made an all-ebony bass for a customer, too. Same report - crazy heavy but crazy sustain, too.